My sculpting tool is not changing my model but I can transform (grab, snake hook, etc.)
I ran into a very similar issue. I'm using version 2.91.2 on Windows. Only Grab, Hook and Clay appeared to work for me.
To fix it, I started off by trying everything in this Blender StackExchange answer - Sculpt tool not working - But it didn't help.
Restarting Blender however, did the trick.
I would have answered on question I linked to, which is much easier to find in a Google search, but community rules prevented me from doing so. So happy days if you find this answer, and it works for you.
Also check your brush tablet pressure settings, just in case:

You'll want to switch them off, when troubleshooting issues with sculpt tools.